1. Field of the Invention
The present invention generally relates to pulse tube cryogenic coolers. More particularly, the present invention relates to a pulse tube cryogenic cooler using a cold storage device cartridge.
2. Description of the Related Art
Generally, a pulse tube cryogenic cooler consisted of a pressure vibration generating device, a cold storage device, a pulse tube, a phase control mechanism, and others. Such a pulse tube cryogenic cooler is quieter than a Gifford McMahon (GM) cryogenic cooler or a Stirling type cryogenic cooler. Therefore, application of the pulse tube cryogenic cooler as a cooling device of various test or analyzing devices such as an electron microscope or a Nuclear Magnetic Resonance (NMR) apparatus has been expected.
FIG. 1 is a structural view of a pulse tube cryogenic cooler of a first related art cases.
Referring to FIG. 1, a pulse tube cryogenic cooler of a first related art case includes a helium compressor 1, a cold storage device 2, a switching valve 3, a phase adjusting mechanism 5, a pulse tube 6, a vacuum flange 7, a cold stage 8, and others.
The helium compressor 1 and the switching valve 3 work as a pressure vibration generating device configured to make helium gas as operation gas generate pressure vibration. The helium compressor 1 and the switching valve 3 are connected to a high temperature end of the cold storage device 2 via a pipe 16.
The switching valve 3 performs a switching operation at a designated cycle so that helium gas having a high pressure and generated by the helium compressor 1 is supplied to the cold storage device 2 at a designated cycle.
The cold storage device 2 is formed by a cold storage device cylinder 10 and a cold storage material 9. The cold storage device cylinder 10 is provided between the vacuum flange 7 and the cold stage 8. The cold storage material 9 is received in the cold storage device cylinder 10.
As the cold storage material 9, for example, a metal fiber or punched metal made of copper, stainless material, or the like may be used. The cold storage material 9 fills the cold storage device cylinder 10 at a designated density.
The operation gas supplied from the helium compressor 1 performs heat exchange with the cold storage material 9 in a period during which the operation gas passes through the cold storage device 2 so that cold storage is performed by the cold storage material 9.
The pulse tube 6 is also provided between the vacuum flange 7 and the cold stage 8. A low temperature end heat exchanger 11 in which a rectifier is provided is provided at a low temperature end of the pulse tube 6. A high temperature end heat exchanger 12 in which a rectifier is provided is provided at a high temperature end of the pulse tube 6.
In addition, a low temperature end of the cold storage device 2 and a low temperature end of the pulse tube 6 are connected by a piercing path 4 formed in the cold stage 8. In the cold storage device 2 and the pulse tube 6, an end part in a direction shown by an arrow X1 in FIG. 1 is a high temperature end. An end part in a direction shown by an arrow X2 in FIG. 1 is a low temperature end.
The phase adjusting mechanism 5 is provided at an upper part of the vacuum flange 7. In addition to the pipe 16, an orifice, a buffer tank, or the like is provided inside the phase adjusting mechanism 5. This orifice or the buffer tank is connected to the high temperature end of the pulse tube 6.
A bottom surface (hereinafter adjusting mechanism bottom surface 15) of the phase adjusting mechanism 5 is directly connected to the high temperature ends of the pulse tube 6 and the cold storage device 2. Therefore, pressure of the operation gas is directly applied. Because of this, the phase adjusting mechanism 5 is tightly fixed to the vacuum flange 7 by using bolts 13.
In addition, a shield member 17 is provided between a flange upper surface 14 and the adjusting mechanism bottom surface 15. The flange upper surface 14 is an upper surface of the vacuum flange. The shield member 17 prevents leakage of the operation gas.
In the above-discussed pulse tube cryogenic cooler, when an operation mode is started, the switching valve is switched so that helium gas compressed by the compressor 1 and having a high pressure flows into the cold storage device 2.
The helium gas flowing in the cold storage device 2 is cooled by the cold storage material 9 provided in the cold storage device 2 so that temperature of the helium gas is decreased. The helium gas flows from the low temperature end of the cold storage device 2 to the low temperature end heat exchanger 11 so as to be further cooled and flows into the pulse tube 6.
Gas having low pressure and already existing in the pulse tube 6 is compressed by the operation gas newly flowing in. Therefore, pressure in the pulse tube 6 becomes higher than pressure in the buffer tank provided in the phase adjusting mechanism 5. Because of this, the operation gas in the pulse tube 6 flows into the buffer tank via the orifice provided in the phase adjusting mechanism 5.
In a receiving mode where the helium has flowed into the pulse tube 6 and the cold storage device 2 is received by the helium compressor 1, the switching valve 3 is switched. As a result of this, the operation gas in the pulse tube 6 flows back into the low temperature end of the cold storage device 2, passes through the cold storage device 2, and is received at the compressor 1 via the high temperature end and the pipe 16.
As discussed above, the phase adjusting mechanism 5 connected to the high temperature end of the pulse tube 6 has the buffer tank and the orifice connected to the pulse tube 6. Because of this, the phase of pressure change and the phase of volume change of the operation gas occur with a constant phase difference.
Due to the phase difference, a cold state as the operation gas is expanded at the low temperature end of the pulse tube 6 is generated. By repeating the above- discussed steps, the pulse tube cryogenic cooler works as a cryogenic cooler.
However, the pulse tube cryogenic cooler shown in FIG. 1 has an integral structure where the cold storage material 9 is directly stuffed into the cold storage device cylinder 10. Accordingly, at the time when the pulse tube cryogenic cooler is operated, if contaminants such as liquid like moisture or the like in helium gas is frozen, loading or blocking may occur in the cold storage material 19. This may cause degradation of cooling ability.
In this case, the temperature of the frozen liquid is increased so that such a frozen liquid may be removed. However, if the contaminants are, for example, oil from the helium compressor 1, even if the temperature of the contaminants is increased, it is difficult to remove the contaminants and therefore it is necessary to exchange the cold storage material 9.
For implementing this maintenance, it is necessary to remove the pulse tube cryogenic cooler from a subject of cooling (not shown in FIG. 1) and exchange the cold storage material 9 for a new one. This causes decrease of an activity rate. In addition, it is necessary to implement a cooling operation again after the cold storage material 9 is changed to the new one. This operation causes increase of cost and time.
In order to solve the above-discussed problem, for example, a pulse tube cryogenic cooler wherein the cold storage material 9 is received in a cold storage device cartridge and this cold storage device cartridge is attached to or detached from the cold storage device cylinder 10 so that cold maintenance can be realized, is suggested in Japanese Laid-Open Patent Application Publication No. 2001-165517.
FIG. 2 is a structural view of a pulse tube cryogenic cooler of a second related art case using a cold storage device 18. In FIG. 2, parts that are the same as the parts shown in FIG. 1 are given the same reference numerals, and explanation thereof is omitted.
The cold storage device cartridge 18 has a closed-end cylindrical shape. The cold storage material 9 fills the inside of the cold storage device cartridge 18.
An opening part 18A is formed in a bottom part 18B of the cold storage device cartridge 18. Therefore, helium gas can flows to or from the pulse tube 6 via the piercing path 4. In addition, a designated gap is formed between the bottom part 18B of the cold storage device cartridge 18 and a container bottom surface 19 of the cold storage device cylinder 10.
However, in the related art cold storage device cartridge type pulse tube cryogenic cooler, in a case where the pressure of helium gas in the cold storage device 2 is increased, the inside of the cold storage device cylinder 10 is connected to the cold storage device cartridge 18 via the opening part 18A.
Because of this, as shown in FIG. 4(A), the pressure of helium gas supplied from the helium compressor 1 is applied to an entire surface of the container bottom surface 19 of the cold storage device cylinder 10.
A force F1 received by the container bottom surface 19 is defined as F1=P×S1, wherein a pressure per a unit area in the cold storage device is “P” and a cross-sectional area of the container bottom surface 19 shown in a dotted manner in FIG. 4(B) is “S1”.
Here, FIG. 4 is a view of a cold storage device cartridge of the pulse tube cryogenic cooler of the second related art cases. More specifically, FIG. 4(A) is an enlarged view of the vicinity of a low temperature end of the cold storage device cartridge and FIG. 4(B) is a cross-sectional view taken along line A-A in FIG. 4(A).
Thus, in the related art cold pulse tube cryogenic cooler, since a pressure receiving area of helium gas (operation gas) in the container bottom surface 19 is large, the force F1 received by the container bottom surface 19 is large.
This force F1 is applied so that the cold stage 8 and the cold storage device cylinder 10 are separated from the phase adjusting mechanism 5. Therefore, the state shown in FIG. 3 is generated in the related art cold pulse tube cryogenic cooler. Here, FIG. 3 is a structural view of the pulse tube cryogenic cooler of the second related art case and shows a state where a vacuum flange is deformed.
As shown in FIG. 3, accompanying an alternating pressure change of helium gas in the cold storage device 2, the cold storage device 2 and the cold stage 8 are deformed alternating in directions shown by arrows X1 and X2. This causes generation of vibration in the pulse tube cryogenic cooler.